Understanding the structure and properties of geological formations can reduce the cost of drilling wells for oil and gas exploration. Measurements made in a borehole (i.e., down-hole measurements) are typically performed to attain this understanding, to identify the composition and distribution of material that surrounds the measurement device down-hole. To obtain such measurements, a variety of sensors are used, including nuclear magnetic resonance (NMR) sensor probes. When used down-hole in conjunction with a magnet and drive electronics, measurements made by the NMR sensor probe can be used to provide information about the surrounding formation.
Generally, nuclear magnetic resonance tools operate by using an imposed static magnetic field and generating this into a material body. This magnetic field is traditionally referred to as the “main magnetic field” or the “static field” as it is usually independent of time and is given the symbol B0. A second magnetic field, which varies in time, is also applied. This field is designated as B1 and is traditionally called the “radio frequency field”. It is turned on and off at different increments, known as a pulse. This perturbing field is usually applied in the form of a radio frequency electromagnetic pulse whose useful magnetic component, B1, is perpendicular to the static field, B0. The perturbing field moves the orientation of the magnetization into the transverse (perpendicular) plane. The frequency of the pulse can be chosen to target specific nuclei (e.g., hydrogen). The polarized nuclei are perturbed simultaneously and, when the perturbation ends, they precess around the static magnetic field gradually re-polarizing to align with the static field once again while losing coherence in the transverse plane. The precessing nuclei generate a detectable radio frequency signal that can be used to measure statistical distributions that can be converted into measurements of porosity (i.e., the relative amount of void space in the formation), hydrocarbon saturation (i.e., the relative percentage of hydrocarbons and water in the formation fluid), and permeability (i.e., the ability of formation fluid to flow from the formation into the wellbore). In the majority of NMR measurements, the B1 magnetic field is created by a coil and is powered by a “transmitter”. This apparatus constitutes a significant draw of energy and, thus, power consumption is a concern. The amount of power which can be delivered down-hole and the degree and accuracy of NMR measurements taken can, accordingly, be limited by this hardware.